Commercial assays for the detection of drugs of abuse in urine change periodically and must be reevaluated for validity of detection. Studies are designed to test the validity of new assays on clinical specimens obtained from drug users under controlled conditions. Healthy male volunteers with a history of chemical substance abuse participate in these studies. Informed consent is obtained and all procedures are approved by the hospital Institutional Review Board. Commercial assays for detection of drugs of abuse in urine are tested for validity with specimens collected under controlled dosing conditions. A variety of drugs of abuse are studied at various dose levels. The results of the assays are compared to GC/MS analyses. These studies test the validity of commercial assays on clinical samples instead of "spiked" samples and provide unique and valuable information to the military and industry concerning their time course of detection, specificity and accuracy.